1. Field of the Invention
The invention relates to structural elements for forming stereochemical models of molecular bonds between multivalent atoms in atomic unions, molecules, molecular aggregates or chemical compounds, the said structural elements each having at least two connector arms representing the valences of at least one atom, each of the connector arms being at one end connected to at least one other of the connector arms, and at least some of the connector arms having in each case a free end which, in order to represent a bond, can be equiaxially coupled with the free end of another of the connector arms of the same structural element or another of the structural elements, manual coupling and uncoupling being possible, and at least one of the said connector arms being connected or able to be coupled to others by an articulating mechanism in such a way as to permit angular adjustment of at least one said connector arm with respect to other connector arms.
2. Description of the Prior Art
In the case of known structural elements of the aforesaid type, the free ends of some connector arms are each shaped as a plug in pin while the free ends of some connector arms other arm are each shaped as a plug-in socket, into which the plug-in pin can be fitted. In the simplest case, some of the connector arms are constructed as rods and some as tubular portions, the rods being capable of being pushed into the tube portions until they reach an abutment or until a snap action locking device is engaged. In other known structural elements, all free ends of the connector arms are constructed as plug in pins. For the coupling of two such connector arms a separate coupling sleeve is required, the free ends of the pin-shaped connector arms to be coupled being inserted into the opposite ends of the sleeve. Further known structural elements for the construction of stereochemical models of molecules have each the shape of a body, for example of a ball, such that instead of having connector arms that can be joined together pairwise, there are holes in these bodies, functioning as plug-in sockets. In this case it is necessary to make use of connecting rods, the opposite ends of which are designed as plug-in pins intended to be inserted into holes of the bodies. Where the known structural elements are concerned, the plug-in pin and plug-in socket or plug-in pins and coupling sleeves or holes and coupling sleeves are all of circular cross-section. Consequently, the structural elements coupled together are capable of rotation about the common axis of the coupling with respect to each other, the resistance to such rotation either being total so that only one position is given or being constant due to even friction, the friction being required to hold the elements together. By reason of the aforesaid rotatability or evenly resisted rotatability, the models of atom bonds or molecules formed from inter-engaged structural elements is either not movable at all of so movable that any connector arms of different structural elements which are not coupled directly to one another may vary their angular orientation on position in space with respect to one another only in an uncontrolled manner.
Also known are structural elements in which at least two connector arms emanating from an atom representing center are mode angularly movable by means of an articulation mechanism, said mechanism however permitting an unlimited number of different angular positions.
The capacity for movement mentioned is actually found in the world of actual chemical compounds and molecular aggregates, but the rotatability of the bonds between pairs of atoms is subject to certain uneven limitations. Definite angular positions tend to occur while other angular positions are only passed through during interconversion of the occurring ones, depending on the three-dimensional configuration of the ligands of the bonded atoms.
To a man skilled in the art of stereochemistry, it is known that two atoms bound together and having each at least one ligand situated at an angle with respect to the bond connecting said two atoms can be rotated with respect to each other about their interconnecting axis and that certain stable angular positions occur, while other are unstable and are only passed through during the said rotation. This partially hindered rotation is called "conformational change".
Also known to a man skilled in the art, is that when there are three or more ligands grouped around a central atom, the ligands may assume certain defined different spatial arrangements, but interconversion between these defined arrangements is possible. The partially hindered interconversion between these defined arrangements of ligands about the central atom is called as "ligand reorganisation" or "pseudo-rotation." Where two mirror-image arrangements are possible, one speaks of an "inversion."
When it is desired to model chemical reactions between molecules or chemical transformations within a molecule, then connector arms of the structural elements of the model representing atomic bonds have to be coupled or separated from to one another in pairs, whereby in many cases one or more of positions above-mentioned angular movements are required at the same time and where it is essential that not all angular positions can be reached with equal probability, since the operation of changing one preferred angular position to another must be performed intentionally, the number of times this is done having to be counted. This is the case, for example, with the model representation of so-called "valence tautomeric" or "pericyclic" reactions, which - particularly in carbon systems - occur stereo-specifically according to the rules of "parity" or "orbital symmetry" known to a man skilled in this field. In these cases, if the sum of the number of times connectors have to be uncoupled (for subsequently being recoupled in different combinations) and of the number of times such angular position changes, for instance inversions, have to be executed is an odd number, it may be concluded that the modelled reaction actually occurs, whereas if this sum is even the modelled reaction does not occur. With the hitherto-known structural elements for forming stereochemical models, the model representation of the said reactions frequently left much to be desired, because the available articulating mechanisms permitted too many angular positions. so that operations of changing the preferred positions cannot be counted. For this reason, it has been difficult hitherto to forecast the structural configuration of products unknown prior thereto.